It looks like it took two years [1], but Optimus Maximus keyboard [2] is for sale! (link via spin the cat [3]) They even have a demo [4] of the keyboard so you can see how it works.
Unfortunately, it's a bit pricey; at $1,600.00, I don't think I'll be getting one any time soon …
[2] http://www.artlebedev.com/everything/optimus/
[3] http://spinthecat.blogspot.com/2007/05/fool-and-his-money-are-soon-parted.html